Unit-handled roller assembly for plastic tubs

ABSTRACT

A unit-handled roller assembly for front loading dishwashers employing a unipartite plastic tub includes a plastic roller mounting stud having an integral annular array of spaced resilient fingers at the tub wall engaging end thereof for maintaining a roller in assembled relationship with the stud prior to installation and serving as an integral washer between the roller and tub wall upon installation. The roller mounting stud also includes an integral, annular sealing ridge upstanding from the tub wall engaging end of the stud in surrounding relation to a central mounting bore for deforming and/or abrading the softer tub wall into fluid tight sealing engagement with the annular ridge. A plurality of the roller mounting assemblies are anchored in a common reinforcing channel member backing a metal collar adjacent the front open end of the dishwasher.

United States Patent [1 1 Afful et al.

[11] 3,804,483 Apr. 16, 1974 UNIT- HANDLED ROLLER ASSEMBLY FOR PLASTIC TUBS 75 Inventors: Matthew K. Artur; David L. Clark,

both of Louisville, Ky.

[73] Assignee: General Electric Company,

Louisville, Ky.

[22] Filed: Dec. 29, 1972 [2]] Appl. No.1 319,348

[52] US. Cl. 312/341 R, 206/46 H [51] Int. Cl A47b 88/00 [58] Field of Search 312/228, 341 R-344;

' 308/18; 248/430; 134/57 D, 58D; 206/46 H [56] References Cited UNITED STATES PATENTS 7/1963 Kendt 308/3.8 6/1965 Dutcher et al.... 3l2/228 l/l971 Kauffman 312/341 R Primary'Examiner -James C. Mitchell Attorney, Agent, or Firm-Francis H. Boos, Jr.

57 ABSTRACT A unit-handled roller assembly for front loading dishwashers employing a unipartite plastic-tub includes a plastic roller mounting stud having an integral annular array of spaced resilient fingers at the tub wall engaging end thereof for maintaining a :roller in assembled relationship with the stud prior to installation and serving as an integral washer between the roller and tub wall upon installation.

The roller mounting stud also includes an integral, annular sealing ridge upstanding from the tub wall engaging end of the stud in surrounding relation to a central mounting bore for deforming and/0r abrading the softer tub wall into fluid tight sealing engagement with the annular ridge.

A plurality of the roller mounting assemblies are anchored in a common reinforcing channel member backing a metal collar adjacent the front open end of v the dishwasher.

15 Claims, 4 Drawing Figures UNIT-HANDLED ROLLER ASSEMBLY FOR PLASTIC TUBS I BACKGROUND OF THE INVENTION The invention is directed to large capacity front loading dishwashers of the type normally comprising a permanent installation and employing upper and lower dish supporting racks as opposed to the smaller, low ca pacity, a portable and/or top loading dishwashers. The reason for the distinction is that the ultimate objective of the invention is the employment of a uniparite plastic tub in large capacity, front loading dishwashers and while some of the problems presented by a proposed use of such a tub would be common to dishwashers of either type; the majority are distinct. Typical distinctions relate to increasing wall flexibility with increasing area, the absence of encompassing metal housings, greater tub shape complexity and additional interior tub mountings such as dual rack support structures. Accordingly, the ensuing background discussion relates primarily to front loading dishwashers of the type normally adapted for a permanent, under cabinet, installation.

The high temperature, corrosive environment to which automatic dishwasher chambers are subjected dictates that the surfaces of those internal components in contact with such environment be either highly resistant, or immune, to corrosion. Corrosion resistant metals such as stainless steel represent a substantial cost factor in this highly competitive appliance field and the long term industry trend has been toward theme of inert materials to resist the corrosive effects of the chamberenvironment which are magnified adjacent the usual metal tub seam welds. lnsofar as the tub itself, representing the far greater internal surface areacxposure, is concerned; the general trend in the United States has been toward the'application of an adherent plastic coating to the tub interior while European manufacturers have gone more to the use of plastictub liners. In either event, the basic structural and design pa rameters that have prevailed since the advent of the modern front loading automatic dishwasher remained valid. This for the reason that overall dishwasher design parameters, both as regards utility and structural integrity, are virtually unaffected by whether the conventional metal tub is coated, lined or exposed.

Conceptually, the use of a unipartite plastic dishwasher tub, i.e., one not requiring a more rigid backing or outer support structure, represents a substantial advance in the art. Exemplary are the greatly decreased cost factors of a molded plastic tub vis-a-vis that of a metal tub requiringa further coating or lining operation; reduction in finishing labor requirements and particularly tub welding operations; longer tub life due to corrosion resistance which is independent of faulty coating procedures or chipping; decreased thermal and acoustical transmission thus minimizing the need for separate insulation; and a lesser inventory requirement for separable components susceptible of integral molding with the tub.

The reduction to practice of such a concept, as applied to front loading dishwashers on an assembly line basis, however, presents a myriad of problems which arise as a requirement for different approaches to those engineering considerations which had previously been predicated upon the use of a metal tub. The distinctions are primarily those associated with material strength the unusually high temperature environment to which the tub is subjected and considerations relating to plastic'molding procedures. Thus, while the structural integrity of a metallic box beam shape defined by the conventional front loading tub is more than sufficient to resist excessive wall deformation as a function or normal loading forces as during installation, adjustment or use and temperature variations from room ambient to approximately 225F; such normally applied loading forces would, in the absence of appropriate compensating structure, produce unacceptable wall deformation in a like configured plastic tub. Similarly, impact strength is normally of little moment in the design and installation of metallic tubs but is a matter of major 7 concern in plastic tub design. Furthermore, various structural features appearing in a formed plastic tub as an incident of the forming operation create problems not previously associated with metal tub fabrication. Exemplary of the latter distinction are the presence, on the finished product, of mold lines and/or mold retention ribs creating localized areas of decreased impact resistance as well as the usual walll draft to permit re moval of the product, or tub, from the forming mold. One primary disadvantage arising from this necessary wall draft concerns the mounting of the disheasher rack supporting racks in parallel.

in addition to the foregoing considerations which re late primarily to mounting and/or assembly procedures for larger capacity. front loading machines, the desirability of precluding tub discoloration and the desirability for firewall separation of the tub and those electrical components constituting a fire hazard are common to all automatic dishwashing machines. As regards plastic tub discoloration, it is preferred to avoid the use of certain conventional reinforcing strand type fillers, such as chopped strand fiber glass, for the reason that their intersection with the interior plastic surface may provide a bleed path for food stains to permeate the tub structure.

The aforementioned firewall separation is a safety requirement but one which may be used to dual advantage in connection with the construction herein'disclosed, which is basically nothing more than a plastic tub equipped with a door and tub support frame, by uti lizing the necessary firewall construction as a power equipment support.

The prior art suggestions relating to the use of small capacity plastic tubs of the top loading type, as in U. S. Pat. No. 2,691,986 and the use of separate plastic tub components, as in U. S. Pat. Nos. 2,877,778; 3,385,306

and 3,460,878 offer little in the way of guidelines as regards a practical reduction to practice of a large capacity front loading tub for the reason that most of the problems requiring solution are not present in smaller and/or top loading units and particularly those which employ an enveloping metal housing.

The present invention relates to the construction of those roller assemblies used to support the upper dishwasher rack and their mounting to the inner sidewalls of the plastic tub while other of the aformentioned matters are more fully described and claimed in the following, commonly owned, copending applications: which are assigned to the same assignee as is the present invention. Ser. No. 319,556, filed Dec. 29, 1972, for Double, Reversed MOunting Boss for Plastic Tub;

3 Ser. No. 319,201, filed Dec. 29,1972, for l-jll Funnel Construction for PlaEYiETubs; Ser. No. 319,555, filed Dec. 29, 1972, for Thermal Growth Compensation and Mounting for Plastic Dishwasher Tubs;

Ser. No. 319,203, filed Dec. 29, 1972, for Front Loading Dishwasher Employing Plastic Tub Construction; Ser. No. 319, 202, filed Dec. 29, 1972, for Radiused Mold Walls for Plastic Tubs;

Ser. No. 317,368, filed Dec. 22, 1972, for Angled Levelling Foot for Domestic Appliance;

Ser. No. 319,200, filed Dec. 29, 1972, for Torsionally Reinforced, Skeletal Support Frame for Plastic Tubs; Ser. No. 319,557, filed Dec. 29, 1972, for Impact Protection for Plastic Tub Employing Mold Retention Ribs;

Ser. No. 319,199, filed Dec. 29, 1972, for Plastic Tub Wall Alignment for Diswasher Rack Mounting.

Insofar as the mounting of the upper dish rack roller supporting assemblies are concerned; the elimination of the conventional front loading metal tub and the substitution therefor of a plastic tub necessitates the presence of mounting and/or support structure to compensate for those inherent characteristics previously available in the use of a metal tube which include rela tively high abrasion resistance, a modulus of rigidity sufficient to preclude wall deformation and provide secure anchor points for roller assembly mounting, and a box beam tub shape insuring adequate resistance to upper rack loading forces. It is apparent that if the advantages of the invention, as regards decreased cost and weight, are to be retained the necessary mounting and support structure must not, in effect, comprise a confining tub support housing. Rather, a purpose of the invention is to provide an operative, front loading dishwasher unit having a plastic tub whose outer walls comprise the great majority of the outer dishwasher unit construction and would actually be exposed to view prior to installation of the dishwasher unit within an outer decorative housing, which decorative housing may comprise a free standing, portable unit or a permanent undercabinet installation.

Although the tub sidewalls inherently present a relatively soft surface which is subject to abrasion by relatively movable component parts, such as the upper rack supporting rollers; this very characteristic can be used to advantage in sealing the tub interior with respect to the necessary through mounting bores in the tub walls.

SUMMARY OF THE INVENTION It has been found that the requisite structural integrity can be imparted to the overall dishwasher and tub construction through the use of a metal base assembly and a relatively narrow (as compared to the tub depth) metal collar upstanding from the base assembly and extending across the top and sidewalls of the tub immediately adjacent the open end thereof. The front, open end of the tub is then secured to the surrounding, composite box beam collar and base assembly thus anchoring the open end of the tub to a relatively rigid metal shape. The savings in fabrication cost and weight involved in bending a narrow metal strap into an approximate U-shape to form a collar and then joining the same to a base assembly as compared with the utilization of a complex metal shape to either form the tub or envelope a tub liner are obvious. The tub itself is comprised of an injection molded, homogeneous, unipartite polypropylene based plastic.

In front loading dishwashers of the type herein disclosed, upper rack loads of 40 pounds are common as is multiple daily usage over an expected dishwasher and tub lifetime in excess of ten years. It is thus apparent that the tub walls, per se, having an exemplary wall thickness of less than 0.2 inch cannot be expected to support the upper rack mounting tracks both by reason of wall deformation under such loads and inherent cold flow characteristics. As regards the latter, reference is had to the presence of track and/or roller mounting bores which, if supported solely by the plastic sidewalls, would fish tail or enlarge under repeated loading impact. The problems of mounting bore enalargement and wall deformation areaccommodated by positioning the anchored supports for the upper rack structure immediately adjacent the open end of the tub so that the supporting fasteners pass thorugh the encompassing metal collar to find rigid anchorage relative thereto rather than in the tub sidewlls. In line with the obvious desideratum of mounting collar formation from as light gauge metal as is consistent with the performance of those supporting roles discussed, supra; separable reinforcing elements are provided to back the roller assembly mountings to the encompassing collar. More specifically, the roller assemblies are mounted, in pairs, to a common channel member backing the mounting collar to spread torque loads and transfer the primary loading forces from the mounting fastener bore walls in the metal collar to corresponding bore walls in the heavier gauge, backing channels.

The mounting of the relatively movable rollers in immediate proximity to the inner tub sidewalls requires the presence of an intermediate bearing structure to avoid abrasion of the relatively soft" plastic walls. Such a function would normally be served by a separable washer which, however, is undesirable from an assembly standpoint as is the usual multistep installation of a roller assembly. The utilization of a roller mounting stud having integrally formed, resilient fingers effectively defining a washer obviates the necessity for separate washer installation and permits the preassembly of a roller with the mounting stud which is retained thereon, to form a unit handled assembly, by the particular washer disposition, acting as a retainer, prior to installation.

The tub engaging end wall of the roller mounting stud is formed with an integral ridge surrounding a central mounting bore which, upon assembly and tightening engagement with a plastic tub wall, abrades and/or deforms the softer tub wall to effect a fluid tight seal around the tub wall mounting bore.

DESCRIPTION OF THE DRAWING FIG. 1 is a broken, front perspective of a front loading dishwasher employing a plastic tub and illustrating the mounting and placement of supporting roller assemblies for an upper dish rack, with the upper rack being omitted for clarity of illustration;

FIG. 2 is a section through one roller assembly taken along line 22 of FIG. 1; FIG. 2A is an alternate form for a component shown in FIG. 2; and

FIG. 3 is an exploded perspective of a roller assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 is illustrated a' front loading dishwasher having a unipartite, plastic tub 12 mounted to metal tub support frame 14 comprising base assembly 16 and mounting collar 18 which mounting collar encompasses, in backing relation, and is secured to the top and sidewalls 20, 22 of tub 12 immediately adjacent the forward open end thereof as by fasteners 24. It will be noted that in line with a primary purpose of the invention to eliminate any semblance of a metal tub or corresponding housing, the width of the mounting collar is kept as small as is consistent with its required role of imparting to the open tub front the necessary rigidity. Accordingly, all of the upper rack supporting rollers are grouped immediately adjacent the front end of the tub to permit this anchorage in mounting collar 18.

The roller assemblies 26 are grouped in spaced, paired relation on opposed tub sidewalls 22 with each vertically related pair being anchored to a common reinforcing channel element 28 backing mounting collar 18. As will be apparent from the foregoing discussion, the torque loads imparted to the roller assemblies upon maximum extension of the upper rack (not shown) via the rack supporting track 30 are substantial. The transfer of these loads via the relatively heavy bore walls 32 of reinforcing element 28 to an extended surface area of the mounting collar permits the utilization of lighter gauge sheet metal for the mounting collar than would be required for rigid support of the roller assemblies through the mounting collar bore walls 34 and immediately surrounding surface area.

The tub wall mounting bores 36 for the various roller assemblies are sealed with respect to the tub interior by the embedment, in tub wall 22, of annular sealing ridges 38 integral with the tub wall engaging ends 40 of the various mounting studs 42 on which track supporting rollers 44 are journalled. In actuality, the seal surrounding tub wall mounting bore 36 is achieved by a combination of tub wall abrasion and wall deformation since the usual assembly procedure involves running the mounting stud 42 down on its supporting fastener 46 as by rotation of the stud via hex faces 48. Continued rotation of the stud after initial contact between annular ridge 38 and tub sidewall 22 results in abrasion and'cleformation of the sidewall until the sealing ridge is fully embedded as illustrated in FIG. 2. If the mounting stud is drawn up by rotation of fastener 46 then the sealing effect and at least partial embedment of the sealing ridge would be as a result of cold flow or wall surface deformation.

An annular array of spaced, resilient fingers 50, having outer surfaces continuous with the cylindrical bearing surface 52, are formed integral with mounting stud 42 and extend beyond the tub wall engaging end thereof. These fingers 50 are readily flexible between the initially formed, dotted line poisitions of FIG. 3 wherein the outer surfaces thereof define a straight angle with bearing surface 52 and a position displaced 90 therefrom as indicated in the roller assembly installation of FIG. 2, to collectively define a washer" or wear surface intermediate roller 44 and tub wall 22. Additionally, these fingers define an integral retainer for roller 44 prior to tub wall installation of the assembly as the fingers assume an outwardly flared bias, indicated in solid lines in FIG. 3, which is mechanically imparted thereto following their emergence through the studmounting bore 54 in roller 44. The fingers may, for example, be deformed to the solid line position of FIG. 3 by jamming the tub wall. engaging ends 40 of the studs against a flat surface following assembly of the roller. The roller is thus maintained in unit-handled relation on the mounting stud by opposed retainers at opposite ends of bearing surface 52 comprised of the relatively rigid stop shoulder 56 andthe deformed, resilient fingers 50. A partial insertion of threaded fastener 46 into stud mounting bore 58 results in a three-part unit handled assembly which requires removal of the fastener prior to assembly with the dishwasher Preferably, the fasteners 46 are permanently secured to their respective channels 28, such as by welding or the like, so that tub installation only requires manipulation of a channel 28 to insert its two attached fasteners 46 through the mounting bores and then running down the roller assemblies on the fasteners. As the tub engaging end 40 of mounting stud'42 approaches the tub wall, the bevelled ends 60 of fingers 50 cam the fingers outwardly and further tightening of the roller mounting stud results in the movement of fingers'50 to the position of FIG. 2 whereupon the same are perpendicualr to the axis of roller 44 and define a washer bearing surface separating the roller and tub wall. Desirably, the plastic roller assembly components have a higher hardness rating than the plastic tub. 7 Having heretofore described the preferred embodiment of this invention in detail, an alternative form for the mounting stud 42 may be described with reference to FIG. 2A. The array of resilient fingers 50 project circumferentially from the mounting stud and serve as an annular deformable means adapted to retain the roller in unit-handled relation with the stud prior to installation and then deform to serve as a thrust washer after installation. An alternate embodiment of the means for retaining the roller on the stud and serving thereafter as an integral thrust washer may be a continuous circumferentially projecting substantially thin deformable web portion 62 as shown in FIG. 2A. Initially, the web portion may be moldably formed as an annular projection parallel to the axis of the stud which may then be flared outwardly generally to the configuration shown in FIG. 2A to retain the roller on the stud. Deforming the web portion to the aforementioned flared configuration is preferably accomplished by an intermediate step prior to installation of the mounting stud in the dishwasher, using suitable tools therefor. Final seating of the mounting stud in its installed position against the tub wall then serves to further deform the web portion to project directly radially outwardly whereby one surface thereof would be disposed for contact with the edge of the roller adjacent thereto and the other surface thereof would be in abutting contact against the tub wall surface. It is further contemplated that the web portion 62 can be molded to have spaced apart parallel surface depressions or score lines serving as separation guide means whereby, as an incident of installing the mounting stud against the tub wall, the web portion 62 will break along the score lines and thereby transform into the annular finger array heretofore described.

While the background discussion of this specification is related primarily to front-loading dishwashers of the type normally adapted for a permanent undercounter installation as opposed to the type of dishwasher having a hinged top closure for top-loading, it should be emphasized that many such machines are commerically produced and purchased for indefinite use as a freestanding model adaptable at a later time by the owner to a built-in unit beneath a kitchen countertop to blend with the matching cabinet structure of the kitchen. Generally, the difference between the unit designed as a convertible and the unit to be immediately permanently installed is the inclusion of side, rear and top cabinet appearance panels to the basic unit structure as designed for permanent installation. Therefore, it should be understood that the present invention is specifically directed to the front-loading type of dishwasher structure whether of the generally lower-cost ing collar upstanding from the front end thereof and encompassing the top and sidewalls of the tub at the front open end thereof, the improvement comprising: a plurality of unit-handled roller assemblies mounted on opposite sidewalls of said plastic tub and anchored in said tub mounting collar; each said roller assembly including a roller mounting stud having a cyclindrical bearing portion and a roller journalled thereon; one end of said cylindrical bearing portion terminating in a tub wall engaging end surrounded by an annular array of spaced resilient fingers lying substantially at right angles to the axis of said cylindrical bearing portion to lie intermediate said roller and tub sidewall; and said annular finger array having opposite surfaces thereof engaged by said tub wall and roller, respectively.

2. The combination of claim 1 wherein said roller mounting stud and annular finger array are of integral plastic construction and have a higher hardness rating than said plastic tub.

3. The combination of claim 2 wherein one surface of each of said spaced fingers is continuous with the surface of said cylindrical bearing portion.

4. A unit-handled roller assembly having an integral roller mounting stud and washer, comprisingz'a roller mounting stud having a cylindrical bearing surface and a roller journalled thereon, means on one end of said stud for retaning said roller thereon, the opposite end of said stud comprising integral circumferentially extending annular deformable means adapted to retain said roller in unit-handled relation with said mounting stud prior to installation at which time the deformable means flexes into substantially perpendicular projecting relation to the axis of said roller to comprise a thrust washer therefor.

5. The assembly of claim 4 wherein said deformable means projects, in its installed position, radially outwardly beyond the edge of said roller adjacent thereto.

6. The assembly of claim 4 wherein said mounting stud is plastic.

7. The assembly of claim 4 wherein said retaining means on said one end of said mounting stud is integral to said mounting stud. 8; The assembly of claim 4 wherein said deformable means comprises an annular continuous web portion disposed in an outwardly flared configuration prior to installation, and said web portion being deformable to project radially outwardly as an incident of installation of said mounting stud.

9. The assembly of claim 8 wherein one surface of said web portion is continuous with said cylindrical bearing surface of said mounting stud.

10. The assembly of claim 4 wherein said deformable means comprises an annular array of spaced resilient fingers.

11. The assembly of claim 10 wherein the spaced resilient fingers have surfaces continuous with the outer surface of .said mounting stud.

12. In combination with a front loading dishwasher having a tub of generally rectangular cross-section, the improvement comprising: a plurality of unit-handled roller assemblies mounted on opposite sidewalls of said tub; each said roller assembly including a roller mounting stud having a cylindrical bearing portion and a roller journalled thereon; one end of said cylindrical bearing portion terminating in a tub wall engaging end having an integral annular deformable end bearing means projecting radially outwardly in contact with said tub wall.

13. The combination of claim 12 wherein said end bearing means is an annular array of spaced resilient fingers.

14. The combination of claim 13 wherein one surface of each of said spaced fingers is continuous with the surface of said cylindrical bearing portion.

15. The combination of claim 13 wherein said annular fingers each have opposite surfaces engaged by said tub wall and said roller, respectively. 

1. In combination with a front loading dishwasher having a plastic tub of generally rectangular cross-section; a metal tub support frame including a base assembly underlying the lower tub wall and a tub mounting collar upstanding from the front end thereof and encompassing the top and sidewalls of the tub at the front open end thereof, the improvement comprising: a plurality of unit-handled roller assemblies mounted on opposite sidewalls of said plastic tub and anchored in said tub mounting collar; each said roller assembly including a roller mounting stud having a cyclindrical bearing portion and a roller journalled thereon; one end of said cylindrical bearing portion terminating in a tub wall engaging end surrounded by an annular array of spaced resilient fingers lying substantially at right angles to the axis of said cylindrical bearing portion to lie intermediate said roLler and tub sidewall; and said annular finger array having opposite surfaces thereof engaged by said tub wall and roller, respectively.
 2. The combination of claim 1 wherein said roller mounting stud and annular finger array are of integral plastic construction and have a higher hardness rating than said plastic tub.
 3. The combination of claim 2 wherein one surface of each of said spaced fingers is continuous with the surface of said cylindrical bearing portion.
 4. A unit-handled roller assembly having an integral roller mounting stud and washer, comprising: a roller mounting stud having a cylindrical bearing surface and a roller journalled thereon, means on one end of said stud for retaning said roller thereon, the opposite end of said stud comprising integral circumferentially extending annular deformable means adapted to retain said roller in unit-handled relation with said mounting stud prior to installation at which time the deformable means flexes into substantially perpendicular projecting relation to the axis of said roller to comprise a thrust washer therefor.
 5. The assembly of claim 4 wherein said deformable means projects, in its installed position, radially outwardly beyond the edge of said roller adjacent thereto.
 6. The assembly of claim 4 wherein said mounting stud is plastic.
 7. The assembly of claim 4 wherein said retaining means on said one end of said mounting stud is integral to said mounting stud.
 8. The assembly of claim 4 wherein said deformable means comprises an annular continuous web portion disposed in an outwardly flared configuration prior to installation, and said web portion being deformable to project radially outwardly as an incident of installation of said mounting stud.
 9. The assembly of claim 8 wherein one surface of said web portion is continuous with said cylindrical bearing surface of said mounting stud.
 10. The assembly of claim 4 wherein said deformable means comprises an annular array of spaced resilient fingers.
 11. The assembly of claim 10 wherein the spaced resilient fingers have surfaces continuous with the outer surface of said mounting stud.
 12. In combination with a front loading dishwasher having a tub of generally rectangular cross-section, the improvement comprising: a plurality of unit-handled roller assemblies mounted on opposite sidewalls of said tub; each said roller assembly including a roller mounting stud having a cylindrical bearing portion and a roller journalled thereon; one end of said cylindrical bearing portion terminating in a tub wall engaging end having an integral annular deformable end bearing means projecting radially outwardly in contact with said tub wall.
 13. The combination of claim 12 wherein said end bearing means is an annular array of spaced resilient fingers.
 14. The combination of claim 13 wherein one surface of each of said spaced fingers is continuous with the surface of said cylindrical bearing portion.
 15. The combination of claim 13 wherein said annular fingers each have opposite surfaces engaged by said tub wall and said roller, respectively. 